The invention relates to a swing system and a construction machinery or a vehicle, particularly an excavator or a crane, comprising a swing system.
It is known in the art that the upper-carriage of an excavator is moving against the undercarriage (chassis) with a rotational movement called “swing” movement, controlled by the operator via a control lever called “joystick”. Such a known swing system 100 is shown in FIG. 2. In the Figure a hydraulic manipulator 26 embodied as a joystick controls the rotational movement of the upper-carriage of an excavator relative to the undercarriage of the excavator. This rotational movement can be to the left-hand side or to the right-hand side direction.
In a so called “closed loop” system, the swing system 100 is actuated by a swing motor 12, for instance a fixed displacement piston motor, which includes a swing brake system 32, for instance comprising a multi-discs brake 32a which is applied via a brake cylinder and spring 32b when no control pressure is present, and a swing pump 10, e.g. a variable displacement piston pump comprising a swash plate 10a, the displacement of which is controlled by the joystick signal to a swash plate control device 24. The maximum working pressure of the swing system is limited by two pressure relief valves 18. The swing system 100 includes a charging pump 14 which is maintaining the pressure in this arrangement through two charging valves 16 to prevent cavitations. The pressure relief valves 18 and the charging valves 16 are arranged in parallel to each other and connected to the right-hand side and the left hand side of swing pump 10 and the swing motor 12.
The charging pump 14 can also be used as a pressure supply to a servo system of the excavator that is supposed to supply additional hydraulic pressure for example for the operation of the hydraulic manipulator 26 or for releasing of the swing brake 32a through a time delay valve 30.
The charging pressure, typically 20 to 40 bars, is limited by a pressure relief valve 20, and the charging oil is supplied to the components through a filter 22 for better reliability of the system.
The hydraulic pressure of the hydraulic components such as the charging pump 14, the swing pump 10, the swing motor 12, the pressure relief valve 20, the manipulator 26 and the time delay valve 30 can be released into a common tank T or into a multitude of tanks.
By way of example, a time delay typically between 3 to 7 seconds to apply the swing brake 32a in case of no use of the manipulator 26 is made by the time delay valve 30; The time delay valve 30 collects the signal from the hydraulic manipulator 26 via a shuttle valve 28.
When the joystick signal is above a threshold, typically above e.g. 5 bars, the time delay valve 30 supplies a servo pressure to the swing brake 32a which is then released, providing a free swing movement.
When the joystick signal is below the threshold, the time delay valve 30 will throttle the oil going from the swing brake 32a to the tank T, thus generating a certain time delay the length of which is depending on the oil viscosity and the volume of oil in the swing brake system 32.
In such a conventional “closed loop” system any additional torque induced for instance by the attachment load of the excavator standing or driving on a slope is compensated by a counter torque induced by the swing pump 10 and the swing motor 12 until eventually the swing brake 32 system of the swing motor 12 is applied. The swing brake 32a applies automatically after a certain time of non-usage of the swing operation, typically after 3 to 7 seconds.
The hydraulic system of the swing motor 12 and the swing pump 10 has internal leakages. In case the excavator is in a non-horizontal position (for instance when standing or driving on a slope) these leakages (and the gravitation force) may eventually cause the upper-carriage of the excavator to change its position (to “drift”) in a rotational manner relative to the under-carriage of the excavator with time when the swing brake 32a is not applied. The speed of the movement depends on the amount of internal leakage. However, in some working conditions, the operator needs to keep the position of the upper-carriage relative to the under-carriage without being disturbed by such an unwanted drift movement of the upper-carriage.
For this purpose, a manual way to apply the swing brake 32a by actuating an electric switch or pedal, for example, may be provided to the operator (not shown). However, this requires the operator to apply the swing brake 32a manually while using the swing system, making the swing operation more difficult.
EP 0056865 A1 discloses a swing system and a method for construction machinery or a vehicle, comprising a swing brake for blocking or unblocking a rotational movement of portion of the construction machinery. The rotational movement is performed by a swing pump and a swing motor, wherein the swing pump can be positioned in a neutral position where no rotational movement of the portion of the construction machinery takes place. A brake actuator actually engages the swing brake when the swing pump is positioned in its neutral position.
It is desirable to provide a swing system whose swing brake system facilitates a swing operation and provides a more comfortable handling of the swing system for the operator of a construction machinery or vehicle. It is also desirable to provide a construction machinery or vehicle comprising a swing system whose swing brake system facilitates a swing operation and makes it more comfortable for an operator.
A swing system for a construction machinery is proposed, particularly for an excavator or a crane, or a vehicle is proposed comprising a swing brake for blocking or unblocking a rotational movement of a first portion of the construction machinery or vehicle relative to a chassis portion of the construction machinery or vehicle, and comprising a swing pump and a swing motor provided for performing the rotational movement. The swing pump can be positioned in a neutral position where no rotational movement of the first portion of the construction machinery or vehicle takes place (for instance in situations where the rotational movement changes from a right-hand side rotational movement to a left-hand side rotational movement (or vice versa)). At least one brake control actuator is provided for automatically engaging the swing brake when the swing pump is positioned in its neutral position.
According to the invention, a first sensor is coupled to the swing pump for detecting a neutral position of the swing pump where no rotational movement of the first portion takes place (for instance in situations where the rotational movement changes from a right-hand side rotational movement to a left-hand side rotational movement (or vice versa)). The operational state of the swing pump can be detected accurately. The sensor is an angle sensor for detecting a position of a swash plate of the swing pump. The position of the swash plate can be easily accessed.
The expression “construction machinery” includes stationary construction equipment or construction machines as well as mobile construction equipment or construction vehicles.
The swing pump and the swing motor may be adapted and operable to neutralize the effect of a torque induced by a load by applying a corresponding counter torque of equal or almost equal amount and opposite direction.
Favourably, the risk that an unwanted drift of the first portion of the construction machinery or vehicle, e.g. an upper-carriage of an excavator or a crane, relative to an undercarriage of the construction machinery or vehicle will occur, is reduced or even avoided. Such a drift may occur especially when the construction machinery or vehicle is positioned or moving on a slope and has a load attached. The present invention reduces the swing drift of a construction machinery or vehicle, particularly of an excavator of crane, equipped with a closed loop swing system, by automatically applying the swing brake when the upper-carriage should be standing still (i.e. when it should keep its position and orientation relative to the under-carriage on which it is mounted). Further, the brake control actuator according to an aspect of the invention can be easily added to a known swing system, which provides a known swing brake system as described above as a fall back system, or can replace the conventional time delay valve (30 in FIG. 2) which usually activates the swing brake.
The present invention gives the operator a higher comfort by automatically applying the swing brake when the upper-carriage is supposed to be standing still (i.e. not rotating relative to the under-carriage or chassis on which it is mounted), thus considerably reducing or even avoiding the risk of an unwanted drift movement due to internal leakages in the hydraulic system of the swing motor and swing pump. The operator does not need to eventually apply manually the swing brake to overcome the drift. The invention, according to an aspect thereof, provides an improved control of the swing movement in cases where the construction machinery (e.g. excavator or crane) or vehicle is positioned or driving on a slope and thus an improved comfort for the operator.
As the swing drift is significantly reduced (or even avoided) without any human intervention, the construction machinery or vehicle performance is improved, in this case, by reducing (or avoiding) the swing drift. In case of a failure of the at least one brake control actuator, the system can fall back to its known behaviour (where the swing pump and the swing motor will slow down the unwanted drift of the upper-carriage relative to the under-carriage by compensating the additional torque exerted by the load with a corresponding counter torque) with a larger drift but still be operable. Particularly, the at least one brake control actuator can be operated electrically. For instance, the at least one brake control actuator can be a solenoid valve which receives control signals from a control unit, for instance an Electronic Control Unit or abbreviated “ECU”.
According to a favourable embodiment of the invention, the at least one brake control actuator can be electrically controlled for activating or deactivating the swing brake. The electric control is relatively fast so that the swing brake can be applied virtually immediately when required. Particularly, the at least one brake control actuator can be a solenoid valve.
Usually, the rotational movement of the first part of the construction machinery or vehicle is controlled by a manipulator operated by the operator of the construction machinery or vehicle. According to a favourable embodiment of the invention, a control unit can be provided for controlling the at least one brake control actuator depending on the operational state of the swing pump and of the manipulator. Advantageously, such a control unit as well as the at least one brake control actuator and the first sensor for detecting the neutral position of the swing pump can easily be added retroactively to a known swing system.
According to a favourable embodiment of the invention, a second sensor can be provided for detecting an operational state of the manipulator. By identifying the operational state of the manipulator, e.g. a joystick, it can be determined if the neutral position of the swing pump is reached because the swing operation has come to a wanted standstill (state 1) or if the swing direction is changing and the neutral position is only a short and transient position of the swing pump (state 2). In detecting and identifying these two different states the risk of an erroneous and unwanted application of the swing brake in state 2 can be considerably reduced or even be avoided.
According to a favourable embodiment of the invention, the second sensor can be a pressure sensor detecting a pressure caused by activating the manipulator.
Hence, a safe identification of the operational state of the manipulator is possible.
According to a favourable embodiment of the invention, an actuator can be provided for manually activating the at least one brake control actuator for activating the swing brake. The actuator can be located proximate to the manipulator so that the operator can easily cause the swing brake to be applied.
According to a favourable embodiment of the invention, the action of the brake control actuator can be deactivated if the swing pump is outside its neutral position. In doing so, it can be avoided that the swing brake is applied if the swing speed is too high. Expediently, the operation of the brake control actuator can be limited to a pre-determined range or interval of the swing pump displacement close to the zero position of the swing pump, i.e. close to its neutral position where no rotational movement takes place, e.g. to values equally to or less than ±5 degrees around the zero or neutral position, and here in particular to values equally to or less than ±2 degrees around the zero or neutral position, in particular to values equally to or less than ±1 degrees around the zero or neutral position of the swing pump.
According to another aspect of the invention, a method for operating a swing system is proposed, comprising the steps of (i) identifying a neutral position of a swing pump where no rotational movement of the first portion of the construction machinery or vehicle takes place (for instance in situations where the rotational movement changes from a right-hand side rotational movement to a left-hand side rotational movement (or vice versa)), and (ii) activating at least one brake control actuator for automatically engaging a swing brake when the swing pump is in its neutral position. The neutral position of the swing pump where no rotational movement of the first portion of the construction machinery or vehicle takes place is identified by determining a position of a swash plate of the swing pump with an angle sensor.
Advantageously, by applying this method the risk of an unwanted swing drift can be considerably reduced or even be avoided.
According to a favourably method step, an operational state of a manipulator for controlling a rotational movement of a first portion of the vehicle relative to a chassis portion of the vehicle can be identified. The operational state of the manipulator can be used to determine whether the application of the swing brake should be performed or inhibited.
According to a further favourable method step, the swing brake can be applied only if the manipulator is in an inactive operational state. Thereby, the risk of an erroneous and unwanted application of the swing brake at a high speed of the swing movement can be considerably reduced or even be avoided.
According to a further favourable method step, an activation of the swing brake by the operator can be blocked if the swing pump is outside its neutral position. However, the operator may manually engage the swing brake, e.g. via a separate switch arranged on or near the manipulator. Thus, application of the swing brake can be prevented when the swing movement passes zero without any intention of the operator to stop there (for example when the swing direction is changing from the right swing to the left swing (or vice versa)). An application of the swing brake in case the actual swing speed is too high can also be prevented (see also above).
According to still another aspect of the invention, a construction machinery is proposed, particularly an excavator, comprising a swing system according to anyone of the above described features of the swing system such feature taken alone or in combination with any of the other features.
The invention, according to an aspect thereof, can be applied to construction machinery such as excavators or cranes, or any other vehicle or part of it which perform a swing movement or rotational movement. The vehicles can be wheel-borne, track-borne or running on rails. The construction machinery can also be wheel-borne, track-borne or running on rails or stationary.